1. Field of the Invention
The present invention pertains to the packet technology known as Asynchronous Transfer Mode (ATM), and particularly to a monitoring technique for a multi-staged ATM node.
2. Related Art and Other Considerations
The increasing interest for high band services such as multimedia applications, video on demand, video telephone, and teleconferencing has motivated development of the Broadband Integrated Service Digital Network (B-ISDN). B-ISDN is based on a technology know as Asynchronous Transfer Mode (ATM), and offers considerable extension of telecommunications capabilities.
ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and traditionally have a fixed size. A traditional ATM cell comprises 53 octets, five of which form a header and forty eight of which constitute a xe2x80x9cpayloadxe2x80x9d or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
At its termination points, an ATM network is connected to terminal equipment, e.g., ATM network users. Typically between ATM network termination points there are plural switching nodes, the switching nodes having ports which are connected together by physical transmission paths or links. Thus, in traveling from an originating terminal equipment to a destination terminal equipment, ATM cells forming a message may travel through several switching nodes.
A switching node has a plurality of ports, each of which can be connected a link circuit and a link to another node. The link circuit performs packaging of the cells according to the particular protocol in use on the link. A cell incoming to a switching node may enter the switching node at a first port and exit from a second port via a link circuit onto a link connected to another node. Each link can carry cells for plural connections, a connection being e.g., a transmission between a calling subscriber or party and a called subscriber or party.
The switching nodes each typically have several functional parts, a primary of which is a switch core. The switch core essentially functions like a cross-connect between ports of the switch. Paths internal to the switch core are selectively controlled so that particular ports of the switch are connected together to allow a message ultimately to travel from an ingress side of the switch to an egress side of the switch, and ultimately from the originating terminal equipment to the destination terminal equipment.
U.S. Pat. No. 5,467,347 to Petersen discloses an ATM switch in which various types of ATM cells are transmitted between a switch core and ports of the switch. The types of cells include traffic cells, operation and maintenance (OAM) cells, and idle cells.
In general, there are two types of errors that can occur in digital hardware (e.g., an ATM link): hard errors and soft errors. A soft error is intermittent and can seem to disappear after some time. Soft errors often occur during bad conditions or when a link is about ready to break down. A user traversing data through a connection suffering soft errors will see a higher, and mostly unacceptable, bit error rate (BER). It is often quite tricky to find soft errors, since it is usually not sufficient merely to send a short stream of test data through the connection. To detect one bit fault can require much time, although it is usually not acceptable to occupy the connection for test purposes for such a long duration.
Performance monitoring to handle soft errors in links external to an ATM node has been proposed, for example, in ITU-T Recommendation I.610, entitled xe2x80x9cThe Principles of Operation and Maintenance Functions of Broadband ISDNxe2x80x9d. However, there are no standards developed for monitoring connections inside ATM switch fabrics, and it is doubtful that ATM switch manufacturers have much monitoring inside ATM switch fabrics. However, when ATM switches are employed for complex applications such as for a radio network controller of a mobile telecommunications system, for example, which potentially serves hundreds of thousands of connections, performance monitoring is imperative.
For such complex applications, for example, the inventor of the present invention envisions multi-staged ATM nodes comprising two or more ATM switches. What is needed in such nodes, and an object of the present invention, is a technique for selective monitoring ATM segments between interfaces in such nodes.
A multi-stage ATM node comprises plural ATM switches connected together in cascading fashion. A connection setup manager appends a tag to cells which are to be routed through the ATM node. The tag comprises, e.g., a transfer list of destination addresses for routing of the cell through the ATM node. In one embodiment, each of the plural ATM switches has a switch core situated between two switch port interface modules.
For monitoring purposes, a node performance monitoring manager, acting through an originating monitoring unit, defines one or more segments of monitored cell travel through the plural ATM switches of the ATM node, and then selectively activates and deactivates monitoring with respect to the defined segment. A segment can be, for example, a path through the node from a switch port interface module of a first ATM switch to a switch port interface module of a second ATM switch. A terminating monitoring unit at a terminating end of the segment uses the tag of a received cell to determine whether the received cell is subject to performance monitoring, and also prepares a termination unit report regarding cells which are subject to performance monitoring.
For establishing a monitoring segment, the node performance manager generates monitoring management cells, also known as monitoring control cells or control cells. The monitoring management cells also have a tag with a transfer list. The monitoring management cells involved in establishing a monitoring segment are of three types. A first type of such monitoring management cell is a monitoring activation cell which is sent from the originating end of the segment to notify the terminating end that performance monitoring has been activated. The monitoring activation cell specifies, in a data field in its payload, a transfer list which is to be used for setting up the performance monitoring operation as well as an indication of a certain quality of service involved in the performance monitoring. A second of the monitoring management cells is a response cell which is sent from the terminating end of the segment to confirm to the originating end that the terminating end is ready for performance monitoring. A third of the of the monitoring management cells is a monitoring result cell which is sent from the terminating end of the segment to the originating end and which includes monitoring data. The monitoring data can be any conventional diagnostic monitoring information, such as cell count and total checksum, for example.
The node performance monitoring manager also causes generation of monitoring management cells for the purpose of indicating whether monitoring is to start or stop with respect to an already-established segment so that selective blocks of cells can be monitored. These xe2x80x9cstartxe2x80x9d and xe2x80x9cstopxe2x80x9d monitoring management cells also include a tag, with the tag bearing a code indicating whether the monitoring management cell starts or stops the monitoring on the segment. Upon receipt at the originating monitoring unit of the monitoring data which comprises the termination unit report prepared by the terminating monitoring unit, the originating monitoring unit performs an analysis and forwards the analysis results to the node performance monitoring manager. The node performance monitoring manager thereby obtains performance monitoring information with respect to each of the selected segments of the multi-staged ATM node.